In recent years, an organic light-emitting panel, which utilizes electroluminescence of an organic material, has been proposed for use as a display panel in a display device such as a digital television. An organic light-emitting panel typically includes organic light-emitting elements of red (R), green (G), and blue (B) colors arranged in a matrix. The organic light-emitting elements, which are each of one of the aforementioned colors, each include a reflective electrode, a transparent electrode arranged in opposition to the reflective electrode, and an organic light-emitting layer of a corresponding color located between the reflective electrode and the transparent electrode.
In the field of organic light-emitting panels, various arts are known for improving light-extraction efficiency (ratio of output luminance to input electrical power) of an organic light-emitting element through optical design. In particular, Patent Literature 1-3 each propose an art for improving light-extraction efficiency of an organic light-emitting element by providing an optical adjustment layer at a light-extraction side of the organic light-emitting element.
For example, Patent Literature 1 discloses an organic electroluminescence (EL) element array including a reflective electrode, an organic compound layer, a transparent electrode, an optical path length adjustment layer, and a transparent layer. In Patent Literature 1 a microresonator structure is configured by an interface between the reflective electrode and the organic compound layer, and by an interface between the optical path length adjustment layer and the transparent layer, through setting a difference between respective refractive indices of the optical path length adjustment layer and the transparent layer as greater than a difference between respective refractive indices of the optical path length adjustment layer and the transparent electrode (refer to paragraphs 0014 and 0027, and claim 1).
Patent Literature 2 discloses an organic EL element including a metal electrode, an EL layer, a transparent electrode, a high refractive index layer, a low refractive index layer, and a transparent base, wherein a refractive index of the high refractive index layer is set as greater than “refractive index of the transparent electrode minus 0.2” (refer to paragraphs 0013, and 0020-0023).
Patent Literature 3 discloses an organic EL element including a cathode, an electron transport layer, an organic light-emitting layer, a hole transport layer, an anode, an intermediate layer, and a transparent base, wherein a refractive index of the inter mediate layer is set as an intermediate value between a refractive index of the anode and a refractive index of the transparent base (refer to paragraphs 0021 and 0022).